As shown in FIG. 18, on the upper perimeter of a metal cap 50, plural of knurl part 51 having a short width slit 51a are formed. Practically, in the case of the metal cap 50 whose outer diameters is 35 to 40 mm, twenty five to thirty of knurl part 51 having the short width slit 51a of about 2 mm long are formed. The function of the knurl part 51 having the short width slits 51a is to prevent the content from spouting out at the opening of the metal cap by somewhat releasing the pressure generated from carbonated drinks outside through the slit 51a of the knurl part 51 when a consumer turns the metal cap 50 in order to open for drinking. In other words, the slits are formed so as to previously release somewhat pressure outside in opening of the cap. More specifically, in FIG. 19, when the metal cap 50 is turned about one forth of the total angle, the contact between the top surface of a curled portion 54 formed on top of the mouth part 53 and the packing 55 attached on the rear surface of the metal cap become loose to yield a gap in between them. The pressure generated from the carbonated drinks is released instantly outside, passing through the gap, through the plural of knurl part 51 with short width slit 51a. In the conventional metal cap, a hem with a bridge is formed under the lower edge, and the bridge is cut by turning of the metal cap when opened.